1. Field of the Invention
The present invention relates to an axial fan having variable pitch fan blades for controlling the air volume or pressure developed.
2. Description of the Prior Art
In large air conditioning installations for multistory buildings and the like the demands or loads upon the air conditioning system constantly vary as portions of the building are temporarily put out of service, as weather conditions change, etc. These load changes are sensed in various ways, such as by detecting changes in the volume of air passing through the air conditioning fan, or by detecting pressure changes in the main air conduit. Regardless of the sensing means, the load changes sensed must be quickly and automatically compensated for by changing the output of the air conditioning fan.
One method of the prior art effects compensating adjustments by using inlet vane dampers, but this has proved to be noisy and wasteful of power. Another method adjusts the fan output by automatically varying the pitch of the fan blades, but most of the fans utilizing this approach have been unduly expensive, complex, difficult to maintain, and characterized by wasteful internal drag.